Houston-based Particle Drilling Technologies Inc. has successfully tested a new drilling system, designed to enhance the rate of penetration through hard rock.Particle-impact drilling (PID) is a closed-loop process in which hardened steel shot particles are injected into the drilling mud, circulated, and recovered from the mud system without allowing the shot to circulate through a rig’s pumps and surface equipment. The process operates under normal rig pump pressures, and the particles entrained with the drilling fluid are accelerated through the nozzles in a specially designed fixed-cutter drillbit (Fig. 1). The particle-impact drilling bit includes fixed PDC cutters and nozzles ...